The FBI warned local election officials across the U.S. to ramp up cyber security measures after uncovering evidence that hackers breached two state election networks, Yahoo News reported Monday.
The FBI Cyber Division issued an alert earlier this month, titled "Targeting Activity Against State Board of Election Systems," which was restricted for "need to know recipients" and disclosed a bureau probe into cyber attacks against two state election websites this summer. One of the attacks led to the "exfiltration," or theft, of voter registration data.
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"It was an eye opener," one senior law enforcement official told Yahoo. "We believe it’s kind of serious, and we’re investigating."
While the FBI alert did not identify the affected states, sources said foreign hackers breached voter registration databases in Arizona and Illinois.
The FBI’s warning came three days after Homeland Security Secretary Jeh Johnson held a conference call with election officials on Aug. 15 to discuss how to make voting systems more secure, offering to provide federal security experts to examine vulnerabilities.
Johnson said the agency was not aware of "specific or credible cyber security threats" to the election at the time.
The alert came as federal authorities are investigating a series of cyber attacks against non-governmental organizations, including the Democratic National Committee, thought to be the work of Russian government hackers.
The FBI suspects the two intrusions were linked. The bureau is investigating whether hackers are attempting to launch widespread attacks against state election networks.
"The FBI is requesting that states contact their Board of Elections and determine if any similar activity to their logs, both inbound and outbound, has been detected," the alert said.
The bureau encouraged state officials to restrict users to have "only the bare minimum set of resources required to perform business tasks."